This invention relates to thaw indicators for frozen foods, to a method for making such indicators and more particularly to thaw indicators which provide an irreversible visual signal to indicate that a product has been exposed to above freezing temperatures.
Foods are frequently frozen in order that they may be preserved for consumption at a later time. If these frozen foods are thawed even for a short period of time, they may be subject to spoiling and at the very least their characteristics may change so that they are undesirable for later use. Accordingly there have been a number of approaches to manufacture and use thaw indicators for frozen foods.
One such approach is disclosed in a U.S. patent of Fahringer No. U.S. Pat. No. 2,852,394. The Fahringer patent discloses a frozen food thaw indicator which is made by dissolving red and blue vegetable dyes in water. Cotton cords are impregnated with the dyes, frozen intertwined and attached to an article of food and placed in a freezer. If the article thaws, the liquid in the cords allows intermixing of the dyes to promote evidence of thawing.
A more recent patent of Cohen U.S. Pat. No. 3,844,718 discloses a frozen food defrosting indicator which incorporates a waterproof transparent capsule containing an indicator which includes indicia printed in water soluble ink on a hydroscopic substance. The indicator is secure to a frozen food shipment to be monitored and the indicator placed in communication with the shipment. If the shipment defrosts, the indicator admits water or water vapor from the shipment irreversibly effecting the appearance of the water-soluble indicia.
Notwithstanding the above, it is presently believed that there may be a relatively large commercial demand for an improved frozen food thaw indicator and a method for making such indicators. Such indicators are believed to be particularly appealing for individuals who freeze their own products for home use since they are relatively easy to make, inexpensive and can be easily prepared while an individual is preparing homegrown vegetables or the like for freezing. The thaw indicator in accordance with the present invention can also be applied to store bought frozen foods to make certain that they do not become thawed and refrozen during power outages or other malfunctions of a freezer or for example if a door to a freezer is inadvertently left open by a child. The thaw indicators in accordance with the present invention are believed to be relatively durable, easily attached to frozen foods and reliable in giving an irreversible indication when a product is partially thawed.
In essence the present invention contemplates a defrosting indicator for frozen foods which can be readily fabricated in an individuals home using readily available materials. The defrosting indicator includes a piece of transparent tape and at least one and preferably more layers of absorbent material. For example, in a preferred embodiment of the invention, multiple layers of relatively absorbent paper such as paper towels, Kleenex tissues or even toilet tissues may be used. The indicator also includes a frozen segment of an ink cartridge disposed between layers of the absorbent material. The ink cartridge which includes a tubular casing containing semi-dried ink as for example of the type used in ball point pens. The absorbent media or material and frozen segment of semi-dried ink are encased in the transparent tape which is then adapted for attachment to a container of frozen foods, as for example by another piece of transparent tape. Then, if the container is partially thawed, the ink will flow out of the tube and form an ink blot on the absorbent media as an irreversible indication that the food may not be safe to eat.
The invention also contemplates a method for making a defrosting indicator. The method which utilizes readily available raw materials includes the step of providing a ball point pen of the type having a pen point, a supply of semi-dried ink and a plastic tube containing the semi-dried ink. The plastic tube, point and semi-dried ink are then subjected to a freezing temperature as for example by being placed in the freezing compartment of a home or other refrigerator or freezer for a period of time which is sufficient to solidify the semi-dried ink. The frozen plastic tube is then removed from the freezer and cut into segments preferably of about one centimeter each. The pen point is discarded. Any ink remaining on the edges of the segments is removed as for example with a cotton ball. The method also includes the step of providing at least one and preferably more sheets of absorbent material which are cut into an appropriate size. The absorbent material may comprise several sheets of paper towel. The segment of frozen ink contained in the portion of the plastic tube is then placed on or between the sheets of absorbent material. In a preferred embodiment of the invention, the segment is placed on top of several sheets of paper towel or the like and the tissue is then folded over to encase the segment. A piece of transparent tape which is sized to be slightly larger than the tissue pocket is provided and the tissue placed on an adhesive side of the transparent tape. The transparent tape preferably overlaps the tissue packet and is folded over to form a seal around the sides of the tissue package. The fourth side is sealed by the fold of the tape. A separate piece of transparent tape is then used to attach the indicator to a frozen food container.